AFDye™ 405 Acid (Alexa Fluor® 405 Acid) is a water-soluble, blue-fluorescent dye that is often used in multi-color applications, including flow cytometry and super-resolution microscopy using STORM. Its excitation is ideally suited for the 407 nm spectral line of the krypton laser or the 408 nm violet laser diode. AFDye™ 405 conjugates are pH-insensitive from pH 4 to pH 10.
The carboxylic acid of AFDye™ 405 is a reagent of choice for the preparation of custom activated esters that often are not commercially available. Examples of such activated esters include sulfo-NHS, TFP (2,3,5,6-Tetrafluorophenol), and STP (4-Sulfo-2,3,5,6-Tetrafluorophenol, Sodium Salt). Another common application for the non-activated carboxylic acid is peptide modification during solid phase synthesis, which usually requires in-situ activation with peptide coupling regents, e.g. HATU. AFDye™ 405 Acid is also often used for control experiments, and for calibration.
AFDye™ 405 is structurally identical to Invitrogen’s Alexa Fluor® Dye 405.